The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to a circumferential hermetic seal between two plastic panels the forms an inflatable bladder for an active bolster.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deploying air bag cushions through various openings, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive.
In a typical structure, an active bolster includes a front wall or panel that faces a vehicle occupant and that is attached to a base wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the base wall may have a zig-zag or accordion region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves even inflation across the panel.
The front and base walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They can be blow molded or injection molded. The front and base walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation as a result of the high pressures during inflation.
From a manufacturing standpoint, welding (such as hot plate, ultrasonic, friction, or laser welding) is a desirable method for attaching the front and base walls. In order to provide welding surfaces, a raised circumferential rib or rampart on one wall may be used to extend into contact with a matching raised rib on the other wall. However, such a weld would have to withstand large shear forces during inflation, and a failure of the weld could result in complete loss of the ability to absorb an impact.